I just had an idea which is pretty close to No Man's Sky.
Players have a spaceship and can fly to randomly placed planets, placed and generated with an universal seed.
Upon players entering a planet, it teleports them to a new place/existing place.
With this logic:
Has the planet been visited before?
Then find the place ID for the planet's world and teleport the player to it. Store the player's existing position before teleporting.
If this isn't true:
Generate a new place with the name containing the planet's coords, the universal seed, and the discoverer's name, then teleport the player to it after storing the position.
Entering a planet:
Have a server script use math.noise (cool perlin noise thing added awhile ago), seeded by the planet's position + universal seed which is retrieved with game.Name. math.noise will help generate terrain.
Spawn the player on land next to his landed ship.
Exiting a planet:
Teleport the player back to the main universe place. Load his position which was stored when he entered the planet. Give him a spaceship.
I hope I can manage to script it.